1. Field of the Invention
The present invention relates to locking devices for providing secure entry by use of keys and, more particularly, to a controlled-access lock that allows dual-control by a user key as well as a control key to give complete owner control and security within an immediate time frame.
2. Description of the Background
There is a commercial need to provide controlled key-access security using a control key that sets a lock's accessibility to individual keys, thus providing the owner/operator of a premises with complete control of security. For example, if a tenant key is lost or stolen, the landlord typically must have the door lock replaced at significant expense. This situation is especially acute in multiple-unit buildings such as apartments and office buildings. Electronic key systems now exist to allow an owner to selectively permit one key card to open each lock and not the other key cards. However, these systems are cost prohibitive for many business and residential applications. There currently is no mechanical lock equivalent to provide a cost-effective solution.
There have, however, been a few prior efforts to develop a mechanical controlled-access lock. For example, pin tumbler locks which may be rekeyed without removing the tumblers, and therefore rekeyed without a locksmith, are known. U.S. Pat. No. 1,565,556 of Fremon, issued Dec. 15, 1925, and U.S. Pat. No. 2,603,081, of Pelle, issued Jul. 15, 1952 disclose locks which must be removed from the lock assembly in which they have been assembled in order to effect rekeying. Therefore, while those locks may not require a locksmith for rekeying, rekeying would not ordinarily be attempted by someone who is not mechanically inclined. U.S. Pat. No. 5,921,121 to Tang issued Jul. 13, 1999 shows an adjustable key-type spring pin lock cylinder. By turning an adjusting lever (10) the owner can select one of two keys to open the lock. A lock which may be rekeyed from the exterior by a reset key which adjusts the positioning of the tumblers is disclosed, for example, in U.S. Pat. No. Re. 28,319 of Kerr, which was reissued on Jan. 28, 1975 (original patent issued on Sep. 4, 1973). The '319 Kerr Patent discloses an axial pin tumbler lock which includes a number of pin tumbler sets that extend circumferentially about the lock, each of the tumbler sets including three axially-extending tumblers. One set of circumferentially-extending tumblers is rotated relative to the other two sets by the reset key to form new combinations of three tumblers for each tumbler set, thereby rekeying the lock. The reset key must be inserted into the lock in the same angular position relative to the lock that it was in when it was last withdrawn from the lock, otherwise the lock can not be rekeyed. In order to facilitate proper introduction of the reset key, the '319 Kerr Patent suggests that the front of the lock be marked with indicia to identify the positions of the axial tumbler sets. However, such indicia may distinguish the exterior appearance of the lock from a non-rekeyable lock of the same type and thereby suggest that the lock may be re-keyed.
All of the foregoing prior art examples require modification of the entire lock or some special outward indica. Also, the size of the existing designs make their use in common padlocks prohibitive. Furthermore, the control key merely activates the blocking or re-keying mechanisms in these other designs as opposed to actually opening the lock, and thus control keying is extremely limited in the existing patented designs.
It would be greatly advantageous to provide a main body lock assembly that can be used in existing commercial and residential locks and padlocks containing removable main bodies that allow controlled, reversible security using a control key to set the lock's accessibility to multiple individual keys. The control key should act to limit the lock's accessibility, but remain completely functional in operating the lock at all times.